Embodiments in accordance with the present invention generally relate to methods and apparatuses for use in the fabrication of semiconductor devices, and in particular to gas distribution showerheads employed in high temperature deposition processes.
High temperature chemical vapor deposition (CVD) processes have encountered widespread use in the semiconductor industry. FIG. 1A shows a simplified cross-sectional view of a conventional apparatus for performing high temperature chemical vapor deposition. For purposes of illustration, FIG. 1A, an other figures of present application, are not drawn to scale.
Apparatus 100 comprises wafer support structure 104 housed within deposition chamber 105. A wafer 102 may be placed upon support structure 104 during substrate processing.
Gas distribution showerhead 106 is positioned above wafer 102 and is separated from wafer 102 by gap Y. The magnitude of gap Y for a particular application may be controlled by adjusting the height of wafer support structure 104 relative to showerhead 106. For example, during conventional deposition of undoped silicate glass (USG) materials, gap Y may be greater than about 300 mils.
Gas distribution showerhead 106 comprises process gas inlet 108 in fluid communication with blocker plate 110 having apertures 112. Gas distribution face plate 114 is positioned downstream of blocker plate 110. Face plate 114 receives a flow of process gas from blocker plate 110 and flows this gas through holes 116 to wafer 102. Layer 118 of deposited material is formed over wafer 102 as a result of the flow of process gases.
FIG. 1B shows a bottom perspective view of the conventional gas distribution face plate 114 of FIG. 1A. Holes 116 of face plate 114 are distributed over the surface of the face plate. FIG. 1B shows only one example of the distribution of holes 116 on a face plate, and many other arrangements of holes on a face plate are possible.
Referring again to FIG. 1A, the role of blocker plate 110 is to coarsely distribute incoming process gas stream 120 over the inlet side 114a of face plate 114. Face plate 114 in turn distributes the gas stream to produce a uniform, finely distributed flow that is exposed to wafer 102. As a result of exposure to this finely-distributed flow of processing gas, high quality layer 118 of deposited material is formed over wafer 102.
The conventional high temperature deposition apparatus shown in FIGS. 1A-1B is effective to create structures on the surface of a semiconductor wafer. One type of structure formed by high temperature CVD is shallow trench isolation (STI). FIG. 2 shows an enlarged cross-sectional view of wafer 200 bearing semiconductor structures 202 such as active transistors. Adjacent active semiconductor devices 202 are electronically isolated from one another by STI structures 204 comprising trenches filled with dielectric material such as undoped silicate glass (USG).
STI structures are formed by masking and etching exposed regions of a wafer to create trenches. The mask is then removed and USG is deposited over the wafer using a high temperature process, including within the trenches. USG deposited outside of the trenches may subsequently be removed by etching or chemical mechanical polishing (CMP) to reveal the final STI structures.
The conventional apparatus shown in FIGS. 1A-1B has been successfully utilized to deposit materials such as USG at high temperatures, for STI and other applications. However, improvements in the design of the high temperature deposition apparatus are desirable. For example, it is known that faster deposition rates may be achieved by spacing the showerhead closer to the wafer. A faster deposition rate will enhance throughput of the deposition apparatus, thereby enabling an operator to more quickly recoup costs of purchasing and maintaining the device.
However, closer spacing of the wafer relative to the showerhead can result in the deposited material exhibiting uneven topography visible as spotting or streaking on the wafer. The topography of material deposited at such close wafer-to-showerhead spacings may reflect the location of holes on the faceplate.
FIGS. 3A-3B are photographs illustrating the results of deposition of material in accordance with embodiments of the present invention. FIG. 3A is a photograph showing a wafer bearing a USG film deposited from a conventional showerhead with a face plate-to-wafer spacing of 75 mils. The wafer of FIG. 3A shows significant spots and streaking.
FIG. 3B is a photograph showing a wafer bearing a USG film deposited from a conventional showerhead with a face plate-to-wafer spacing of 50 mils. The wafer of FIG. 3B shows even more pronounced spotting and streaking than the wafer of FIG. 3A.
Accordingly, methods and structures permitting application of processing gases at a close proximity to the surface of a substrate are desirable.
A gas distribution showerhead for semiconductor fabrication applications includes a face plate having gas outlet ports in the form of elongated slots or channels rather than discrete holes. The use of elongated gas outlet ports in accordance with embodiments of the present invention substantially reduces the incidence of undesirable spotting and streaking of deposited material where the showerhead is closely spaced from the wafer. A showerhead having a tapered profile to reduce edge thickness of deposited material is also disclosed.
An embodiment of an apparatus for forming a material on a semiconductor wafer comprises a processing chamber defined by walls, a processing gas supply, and a wafer support positioned within the processing chamber and configured to receive a semiconductor wafer. A gas distribution showerhead overlies and is separated from the wafer support, the gas distribution showerhead comprising a face plate having an inlet portion comprising a hole in fluid communication with an elongated slot of an outlet portion of the face plate, a length of the elongated slot at least twice a thickness of the face plate.
An embodiment of a gas distribution face plate in accordance with the present invention comprises a face plate body having a thickness. An inlet portion of the face plate is configured to receive a flow of a processing gas, the inlet portion comprising an aperture having a width. An outlet portion of the face plate is configured to convey the processing gas flow to a semiconductor wafer, the outlet portion comprising an elongated slot in fluid communication with the aperture, the elongated slot having a length at least twice the thickness of the face plate body.
An apparatus for forming a material on a semiconductor wafer, the apparatus comprising a processing chamber defined by walls; a processing gas supply, and a wafer support positioned within the processing chamber and configured to receive a semiconductor wafer. A gas distribution showerhead overlies the wafer support and includes a tapered face plate proximate to the wafer support, an edge of the tapered face plate exhibiting a reduced thickness relative to a thickness of a center of the face plate, such that material deposited on a wafer in contact with the wafer support exhibits a uniform center-to-edge thickness.
A method of distributing gas during a semiconductor fabrication process comprising flowing a gas from a gas source to an inlet portion of a gas distribution face plate featuring a hole having a width, and flowing the gas from the hole to a surface of a semiconductor wafer through an elongated slot of an outlet portion of a gas distribution face plate, the elongated slot having a length at least twice a thickness of the gas distribution face plate.
These and other embodiments of the present invention, as well as its features and some potential advantages are described in more detail in conjunction with the text below and attached figures.